Taken from Causes and Cancer
Cancer has many causes
There are about 200 different types of cancer affecting all the different body tissues. What affects one body tissue may not affect another. For example, tobacco smoke that you breathe in may help to cause lung cancer. Over exposing your skin to the sun could give you a melanoma on your leg. But the sun won't give you lung cancer and smoking won't give you melanoma.
Apart from infectious diseases, most illnesses are 'multifactorial'. Cancer is no exception. Multifactorial means that there are many factors involved. In other words, there is no single cause for any one type of cancer.
Carcinogens
A 'carcinogen' is something that can help to cause cancer. Tobacco smoke is a powerful carcinogen. But not everyone who smokes gets lung cancer. So there must be other factors at work.
Age
Most types of cancer become more common as we get older. This is because the changes that cause a cell to become cancerous in the first place take a long time to develop. There have to be a number of changes to the genes within a cell before it turns into a cancer cell. The changes can happen by accident when the cell is dividing. Or they can happen because the cell has been damaged by carcinogens and the damage is then passed on to future 'daughter' cells when that cell divides. The longer we live, the more time there is for us to accumulate these genetic mistakes in our cells.
Genetic make up
There have to be a number of genetic mutations within a cell before it becomes cancerous. Sometimes we are born with one of these mutations already. This does not mean we will get cancer. But with one mutation from the outset, it makes it more likely statistically that we will. Doctors call this 'genetic predisposition'.
The BRCA1 and BRCA2 breast cancer genes are examples of genetic predisposition. Women who carry one of these faulty genes have a higher chance of developing breast cancer than women who do not.
The BRCA genes are good examples for another reason. Most women with breast cancer do not have a mutated BRCA1 or BRCA 2 gene. Less than 5% of all breast cancer is due to these genes. So although women with one of these genes are individually more likely to get breast cancer, most breast cancer is not caused by a high risk inherited gene fault.
This is true of other common cancers where some people have a genetic predisposition, for example colon (large bowel) cancer.
Researchers are looking at the genes of people with cancer in a study called SEARCH. They also hope to find out more about how other factors might interact with genes to increase the risk of cancer. Information about this study is on our clinical trials database. Either follow the link or click on the blue button to the left of any CancerHelp UK screen. Then type SEARCH into the Free Text Search box. Please note that you cannot volunteer for this study.
The immune system
People who have problems with their immune systems are more likely to get some forms of cancer. This group includes people who:
Have had organ transplants and take drugs to suppress their immune systems to stop organ rejection
Have AIDS
Are born with rare medical syndromes which affect their immunity
The kinds of extra cancers that affect these groups of people fall into two, overlapping groups:
Cancers that are caused by viruses, such as cervical cancer or some lymphomas
Lymphomas
Chronic infections or transplanted organs can continually stimulate cells to divide. This continual cell division means that immune cells are more likely to acquire mutations and develop into lymphomas.
Diet
Cancer experts estimate that changes to our diet could prevent about one in three cancer deaths in the UK. In the western world, many of us eat too many animal fats and not enough fresh fruit and vegetables. This type of diet is known to increase your risk of cancer. But how exactly we should alter our diets is not clear. There is more about this in the page on diet causing cancer.
Sometimes foods or food additives are blamed for directly causing cancer and described as 'carcinogenic'. This is often a distortion of the truth. Sometimes a food is found to contain a substance that can cause cancer but in such small amounts that we could never eat enough of it to do any harm. And some additives may actually protect us. There is more about food additives in the page on diet causing cancer.
Day to day environment
By this we mean what is around you each day that may help to cause cancer. This could include:
Tobacco smoke
The sun
Natural and man made radiation
Work place hazards
Asbestos
Some of these are avoidable and some aren't. Most are only contributing factors to causing cancers - part of the jigsaw puzzle that scientists are still trying to put together. There is more about this in the page on causes of cancer in the environment .
Viruses
Viruses can help to cause some cancers. But this does not mean that these cancers can be caught like an infection. What happens is that the virus can cause genetic changes in cells that make them more likely to become cancerous.
These cancers and viruses are linked:
Cervical cancer and the genital wart virus, HPV
Primary liver cancer and the Hepatitis B virus
T cell leukaemia in adults and the Human T cell leukaemia virus
There will be people with primary liver cancer and with T cell leukaemia who haven't had the related virus. But infection may increase their risk of getting that particular cancer. With cervical cancer, scientists now believe that everyone with an invasive cervical cancer will have had an HPV infection beforehand.
Many people can be infected with a cancer-causing virus, and never get cancer. The virus only causes cancer in certain situations. Many women get a high risk HPV infection, but never develop cervical cancer. Another example is Epstein-Barr virus (EBV). These are some facts about this common virus:
Most people are infected with EBV
People who catch it late get glandular fever but this does not cause cancer
In sub-Saharan Africa, EBV infection and repeated attacks of malaria together cause a cancer called Burkitt's lymphoma that affects children
In China, EBV infection (together with other unknown factors) causes naso-pharyngeal cancer
In AIDs patients and transplant patients EBV can cause lymphoma
In the UK, about 4 out of 10 cases of Hodgkin's disease seem to be related to EBV infection
Protective and risk factor foods
It is thought that these foods are protective against cancer:
Fruits and vegetables
Fibre
Vitamins A, C, E and D
Certain types of oils found in fish
And these foods are risk factors for cancer:
Fats (especially animal fats)
Red and processed meats
Alcohol
But it's a complicated picture. It does not seem to be enough to take vitamin supplements for example. There is something about eating fresh vitamin rich foods that is protective.
An international research study is going on at the moment across Europe to try to answer more questions about diet and cancer. The study, called EPIC, involves 500,000 people in 10 countries. EPIC stands for European Prospective Investigation into Cancer and Nutrition. The researchers are looking into the food intake of those taking part over many years. They are also monitoring these people's health records and recording who gets cancer and who doesn't. Then they may be able to link certain factors in the diet with the risk of getting particular cancers. It is the largest study into diet and cancer ever conducted.
The results of EPIC could have huge implications for the prevention of cancer. To start with, the researchers are looking into common cancers such as breast, lung, colorectal, prostate and stomach cancer. But the size of this study means that researchers will also be able to look into the possible role of diet in rarer cancers. The results of the study will have implications for cancer prevention everywhere. The results will be presented at international conferences and published in journals available to researchers and health officials throughout the world.
Food additives and cancer
There are many different substances added to commercially prepared foods. But these are not all bad. Some additives stop food from going off and so can help to keep us healthy. A good example of this is a toxin called aflatoxin that comes from a mould. It grows on stored food in hot and humid countries, especially on peanuts. This is known to help cause liver cancer so anything that stops the mould from getting into the nuts is helping to prevent cancer.
Most additives are not thought to affect cancer risk. Colours, flavours and sweeteners are constantly investigated by researchers and if any are thought to be a real risk, they may be withdrawn. Sometimes there is a scare about a particular additive. Some years ago saccharin was claimed to be a carcinogen.
Researchers had found that when it was fed to rats in huge quantities, the rates of cancer in the rats increased. We are very unlikely to eat so much saccharin and so it is unlikely to cause cancer in people, but far fewer foods contain it now than did a few years ago.
Other additives can be a cancer risk. Pickled foods may increase risk of cancer of the stomach and oesophagus (gullet), particularly if they are very salty. This may explain why there are such high rates of stomach and oesophageal cancer in Japan, where salty, pickled foods are popular.
Contaminants
This means chemicals in foods or drinks that are not meant to be there. They could form as a by-product of the manufacturing process, for example.
Nitrosamines are chemicals found in cured meats (bacon and ham, for example) and beer. Nitrosamines have been shown to be carcinogenic so the amount in foods has been cut as much as possible. In brewing, one cause of nitrosamines is a reaction between pollution in the atmosphere and the malted barley that is one of the main ingredients of the beer. The brewing industry has tried to cut the levels of nitrosamines in beer as much as possible. Levels are now much lower than they used to be, but it hasn't been possible to get rid of them completely.
Smoking and barbecueing foods so that they are slightly burnt on the outside causes chemicals called polycyclic aromatic hydrocarbons to form. These chemicals are known to help cause cancer. So in theory barbecueing or cooking over a high heat could increase the cancer risk of meat and fish. But few research studies have shown this.
Frying and baking meat at high temperatures can create chemicals called heterocyclic amines. These may increase risk of cancer of the bowel or gullet (oesophagus). Acrylamide, another chemical that may cause cancer, has been found in foods such as crisps and chips. But there isn't proof yet that these chemicals cause cancer in humans and so there are no grounds for telling people to change cooking or eating habits because of these chemicals. (You should, of course, change your eating habits to include more fruit and veg!)
Obesity and cancer
'Obese' means more than about 25% overweight. It is measured by comparing your weight with your height. There is information about how to work out the right weight for you in CancerHelp UK. Obesity can increase your risk of:
Breast or uterine (womb) cancer if you are a woman
Colon (bowel), oesophageal, kidney and gallbladder cancer
Researchers are not sure how much the risks increase, or exactly why. Breast cancer is hormone linked. Its development is affected by amounts of the sex hormones oestrogen and testosterone. Fatty tissue produces an enzyme called 'aromatase'. Aromatase affects the balance between these hormones and this may explain why being obese affects your risk of breast cancer. Although obesity increases breast cancer risk if you are postmenopausal, it lowers breast cancer risk if you are premenopausal. But risk of breast cancer increases strongly with age, and being obese increases the risk of several cancers as well as other diseases. So it is important to maintain a healthy body weight throughout your life.
Obese people may have increased risk of bowel cancer because they tend to have higher blood sugar levels. This is because they are resistant to insulin.
A healthy diet
The diet thought to help reduce cancer risk is much the same as that recommended for a healthy heart. So you really can make a difference to your health if you:
Eat less meat and animal fats (butter, cream, cheese)
Eat five portions of raw or lightly cooked fruit and vegetables every day (5 portions is about 400g or 1lb in weight)
Eat more fibre
Eat more oily fish (eg salmon, trout, mackerel)
Eat less salt, salty foods, sugar and sugary foods
Eat more cereals, bread, pasta and rice
Don't fry foods and if you use fats in cooking, choose vegetable oils or olive oil not lard or butter
Drink less alcohol